Regenerative hot blast stoves, which generate hot blast by circulating air to a checker chamber having heat stored therein and supply the hot blast to a blast furnace, include an internal-combustion hot blast stove having both a combustion chamber and a checker chamber provided in a cylinder shell and an external-combustion hot blast stove having a combustion chamber and a checker chamber provided in separate cylinder shells so that both the chambers communicate with each other at one ends of both the shells. As a regenerative hot blast stove which can be made at a lower equipment cost than the external-combustion hot blast stove while retaining the performance comparable with the external-combustion hot blast stove, a top-firing hot blast stove having a combustion chamber, which is connected to a burner, provided above a checker chamber is disclosed in Patent Literature 1.
Now, referring to a schematic view of FIG. 7, the structure of a conventional top-firing hot blast stove will be outlined. As shown in the drawing, a conventional top-firing hot blast stove F has a combustion chamber N placed above a checker chamber T. In so-called combustion operation, mixed gas including fuel gas and combustion air supplied from a burner B to the combustion chamber N (X1 direction) ignites and combusts in the process of passing through a burner duct BD, and flows into the combustion chamber N as high-temperature combustion gas. A plurality of the burner ducts BD are provided for the combustion chamber N when two-dimensionally viewed. High-temperature combustion gas flows downward while swirling inside the combustion chamber with a large turning radius. While the combustion gas flows downward in the checker chamber T (X2 direction), the heat of the gas is stored in the checker chamber T, and the combustion gas which has passed through the checker chamber T is exhausted through a gas duct E. Note that the burner B and the burner duct BD are collectively referred to as a burner system in this specification.
In so-called air blasting operation for supplying hot blast to an unshown blast furnace, a shutoff valve V inside the burner duct BD is controlled to be closed so that air of about 150° C. for example is supplied to the checker chamber T through a blast pipe S. In the process of going upward inside the checker chamber T, the air turns into hot blast of about 1200° C. for example, and this hot blast is supplied to the blast furnace through a hot-blast pipe H (X3 direction).
Enhancement in combustion efficiency of the burners mounted on the top-firing hot blast stove is one of the important objects in the technical field concerned. In order to achieve the enhancement in combustion efficiency, it is known that not only preparing mixed gas including sufficiently mixed fuel gas and combustion air but also stabilizing an ignition point are quite important. It is also known that without a stabilized ignition point, the ignition point is fluctuated inside the burner duct or the combustion chamber, which thereby causes oscillating combustion.
In order to stabilize the ignition point, Patent Literature 2 discloses a gas burner for a hot blast stove having a ring-shaped projection provided between a burner and a burner port (burner duct) for stabilizing an ignition position by using an area around the projection as an ignition point. The structure of this hot blast stove gas burner is simulated in FIG. 8.
As shown in the drawing, fuel gas and combustion air supplied through a burner B are mixed inside the burner B or the burner duct BD to generate mixed gas. A ring-shaped projection R is provided at a middle position inside the burner duct BD, and an aperture of the burner duct BD is narrowed by this projection R. Consequently, the burner duct BD has an upstream space BD1 and a downstream space BD2 on a combustion chamber N side, separated by the projection R in a gas flow direction.
Since the ring-shaped projection R is thus provided inside the burner duct BD to narrow the aperture, an area around the projection R tends to serve as an ignition point, and therefore a so-called flame-holding portion is formed in this area. Furthermore, the projection R generates gas turbulence, which further promotes mixing between fuel gas and combustion air.
When the projection R as shown in the drawing is provided at a middle position in the burner duct BD to form a flame-holding portion, the projection R for narrowing the aperture is to be present on the downstream side of the upstream space BD1. Accordingly, if fire is ignited inside the upstream space BD1, gas inside the upstream space BD1 is heated and the volume thereof is rapidly expanded. Due to this rapid gas volume expansion, pressure inside the upstream space BD1 increases, which hinders supply of fuel gas and combustion air from the burner B, and leads to a problem of extinguishing.
When gas supply is hindered and thereby extinguishing occurs, the pressure inside the upstream space BD1 declines. As a result, the hindered supply of the fuel gas and the combustion air is resumed, and fire is ignited again.
Thus, providing the projection R at a middle position inside the burner duct BD causes a so-called “blinking phenomenon” involving repeated ignition and extinguishing, which poses a new problem to be solved.